Apparatus and method for determining objective refraction using wavefront sensing

ABSTRACT

An apparatus for determining the objective refraction of a patient&#39;s eye includes a transparent window and a wavefront measurement device that determines aberrations in a return beam from the patient&#39;s eye after the beam passes through a corrective test lens in the apparatus. The wavefront measurement device outputs an instant display representative of the quality of vision afforded the patient through the test lens. The display can be a representation of a Snellen chart, convoluted with the optical characteristics of the patient&#39;s vision, an overall quality of vision scale or the optical contrast function, all based on the wavefront measurements of the patient&#39;s eye. The examiner may use the display information to conduct a refraction examination and other vision tests without the subjective response from the patient.

FIELD OF THE INVENTION

[0001] The present invention relates generally to methods and apparatusfor determining a person's visual characteristics, and more particularlyto apparatus for determining the refraction of the eye.

BACKGROUND

[0002] Phoropters are apparatus used by optometrists to determine apatient's visual characteristics, so that proper eye diagnoses can bemade and eyewear can be prescribed. In conventional phoropters, apatient looks through the phoropter, in which various test lenses aredisposed, at a target eye chart, referred to as a “Snellen chart”, whilean optometrist moves the test corrective lenses into the patient's fieldof view. In some applications, the target may be positioned at apredetermined distance from the patient. The patient is then asked toverbally compare the quality of the perceived image as afforded by onelens versus the prior lens presented. The optometrist takes note ofeither an improvement or a deterioration in the patient's vision throughsuch lenses. Systematically, the test progresses towards the “best” testlens entirely based on the patient's responses. The lens parameters arethen used as the basis for a prescription for eyewear.

[0003] Unfortunately, as recognized herein the patient can becomefatigued during the process and/or misjudge the vision afforded by thevarious lenses. This can lead to the selection of a less than optimumprescription. Moreover, some patients, such as a very ill or a veryyoung patient, might not be capable of articulating the quality ofvision the various lenses afford the patient.

[0004] Objective methods of determining the patient's refraction errorshave been proposed, but these other methods introduce furthercomplications that are not present when using phoropters. In aretinoscopy method, for example, a streak of light is projected to apatient's retina, and the characteristics of the reflected light at thepatient's corneal plane is analyzed to determine whether the patient ismyopic, or hyperopic, and with or without astigmatism. However, themethod does not provide sufficient accuracy for prescribing spectaclelenses. Consequently, its measurement results are typically used only asa starting point of a standard phoropter measurement.

[0005] Another objective measurement instrument for determiningrefractive errors is an autorefractor, which, owing to its speed of use,is more popular than retinoscopy. To use the autorefractor, a patient isasked to look inside an enclosed box that is part of the autorefractor.A target image is optically projected into patient's eye, and a seriesof lenses is automatically moved into position of the patient's line ofsight to the target, to neutralize the patient's refractive errors(autorefraction). Unfortunately, the measurement outcome often differsfrom the patient's ideal prescription. Accordingly, like retinoscopy,autorefractor outcomes typically are used only as starting points forstandard phoropter measurements.

[0006] Moreover, both retinoscopy and autorefraction fail to account forthe accommodation effect of the patient, that is, for the propensity ofa patient to alter his or her focus or sight to make the best of thevision test. An autorefractor measurement essentially is a snapshot ofthe patient's vision at a particular instant at which the autorefractorhas identified a so-called neutralization point, and at this point if ithappens that the patient focuses his vision for seeing an image at adistance other than what is intended, or if the patient is momentarilylooking elsewhere other than the target, the output of the autorefractoris erroneous. Such deceptive focussing on the part of the patient canarise because the patient is conscious of the working distance insidethe box, and when an image of an object presented to the patient whichis modelled to be located at, e.g., twenty feet, the patientautomatically focusses for an image at a much closer distance, knowingthe actual size of the box. Examination results that include patientaccommodation effects are inaccurate for prescribing spectacle lenses.

[0007] Another limitation of the autorefractor is that the examiner hasno control over which lens is to be used in test. The result is thatrepeated measurements are likely to provide different results for thesame eye from the same patient, which results in laborious and timeconsuming tests and retests when using the device to finalize aprescription. The present invention, having made the above-notedcritical observations, provides the solutions disclosed herein.

SUMMARY OF THE INVENTION

[0008] A phoropter includes plural test lenses that can be disposed intoa line of sight defined between a patient and a target, such that apatient looking at the target perceives light from the lens. A wavefrontmeasurement apparatus is positioned to detect aberrations in lightreturning from the patient. The aberrations are caused by the eye of thepatient.

[0009] In a preferred embodiment, the wavefront measurement apparatusincludes a light source, such as a laser, for generating the light and alight detector that outputs a signal representative of the aberrations.Also, the apparatus includes a processor that receives the signal fromthe light detector and outputs a diagnostic signal representativethereof. The diagnostic signal is useful for generating an imagerepresentative of the test object, and/or for generating at least onevisual display representative of an effectiveness of the lens incorrecting a patient's vision. The visual display can include a barchart, a pie chart, and/or a line chart, and it can be color coded.

[0010] In another aspect, a method for indicating the quality of apatient's vision includes providing a device through which a patient canlook at a target. The method also includes directing a laser beam intothe eye of a patient when the patient looks at the target, and thendetecting aberrations in a wavefront of the light beam as the light beamreturns from the patient's eye. Based on the wavefront, the methodindicates a quality of a patient's vision.

[0011] In still another aspect, a method for indicating the quality of apatient's vision includes providing a device into which a patient canlook, and that generates an instantaneous visual indication of a qualityof a patient's vision.

[0012] In yet another aspect, a device for aiding a practitioner inknowing the integrated effect of a patient's eye and a test lens placedin front of the eye includes means for sensing a wavefront of lightreturning from the eye through the lens. Means are coupled to thewavefront sensing means for generating an indication of the integratedeffect of the eye and the test lens.

[0013] In another aspect, a device for generating an indication of thequality of vision of a patient viewing a target includes a light beamgenerator directing light into the eye of the patient, and a wavefrontsensing device detecting the wavefront in light returned from the eye ofthe patient while the patient is looking at the target. A computingdevice receives input from the wavefront sensing device that isrepresentative of the wavefront. The computing device outputs acontinuous update of at least one of: a point spread function, and amodular transfer function, while the patient is looking at the target. Adisplay device displays at least one of: a simulated image of the targetat the patient's retina, a quality of vision indicator indicating thequality of vision, and a graph indicating a contrast function of thepatient, based at least in part on at least one of the point spreadfunction and the modular transfer function.

[0014] In yet another aspect, a vision quantifying device includes abeamsplitter through which a patient can look at a target. A source oflight emits light into an eye of the patient, which reflects from theeye as a return beam. A processor receives a signal representative of awavefront of the return beam and generates at least one signal inresponse thereto, and a display receives the signal and presents avisual indication of the patient's sight.

[0015] Another aspect of the device is to provide automatic refractionprocess. The patient looks at a target, a test lens is positionedbetween the target and the patient's eye, and in the line of sight ofthe patient. A light beam is directed through the test lens and into thepatient's eye. Using a portion of that light reflected from the surfaceswithin the eye a wavefront profile is reconstructed. From thereconstructed wavefront profile, A quality vision factor (“QVF”) may becalculated. In order to improve the accuracy of the measurements of thepatient's eye, a number of measurements of the returning wavefrontprofile are taken, and the corresponding QVF values for each of themeasurements for that particular test lens, is analyzed. The analysis ofthis data provides for a determination that the correction with thatparticular lens is optimal. If the correction is not optimal, a nexttest lens is selected, and the process is then repeated the next testlens after it is positioned by mechanical means in the patient's line ofsight. On the other hand, if the correction with that particular lens isoptimal, than the process ends and resulting in the proper refractivecorrection having been identified.

[0016] The details of the present invention, both as to its structureand operation, can best be understood in reference to the accompanyingdrawings, in which like reference numerals refer to like parts, and inwhich:

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a perspective view of the present apparatus, in oneintended environment;

[0018]FIG. 2 is a perspective view of the apparatus, showing a patientin phantom;

[0019]FIG. 3 is a block diagram of the components of one preferredapparatus;

[0020]FIG. 4 is a flow chart of the presently preferred logic;

[0021] FIGS. 5-9 are exemplary non-limiting diagrams of quality ofvision displays; and

[0022]FIG. 10 is a flow chart showing the automatic refraction method ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0023] Referring initially to FIGS. 1 and 2, an apparatus of the presentinvention is shown, generally designated 10, and includes a housing 12that can be mounted on a movable stand 14 for positioning the housing 12in front of a patient 15 who might sit in an examination chair 16. Ascan be appreciated in cross-reference to FIGS. 1 and 2, the patient 15can position his or her head against the housing 12. Alternatively, thehousing 12 can be supported on the head of the patient 15 and/or besuspended from a flexible overhanging arm which may be attached to astand, to provide weight balance and to facilitate mounting anddismounting of the head mounted-apparatus. Or, the apparatus of thepresent invention can be co-mounted with a conventional phoropter (notshown), in which case the test lenses of the present invention can beestablished by the lenses of the conventional phoropter.

[0024] Now referring to FIG. 3, the patient 15 can look through thehousing 12 to a target 18, such as but not limited to a Snellen chart.The target 18 can be positioned at any appropriate distance from thepatient 15, e.g., twenty feet or closer. Since the target 18 can bepositioned at a distance that actually is the distance intended, theabove-noted patient accommodation effects related to autorefractors, arereduced or eliminated.

[0025]FIG. 3 shows one exemplary implementation of the housing 12. WhileFIG. 3 shows that various components are located inside the housing 12and various other components such as the output display is locatedoutside the housing 12, it is to be understood that the principlesadvanced herein apply to phoropter systems having multiple housings, ora single housing.

[0026] In the embodiment shown, the patient looks at the target 18through a transparent window within the housing 12, such as can beestablished by a primary beamsplitter 20. Interposed in the line ofsight of the patient 15 are one or more movable test, or test lenses 22.By “movable” is meant physically movable by hand or computer-controlledmechanism “M” as indicated as M in FIG. 3, and more fully disclosedbelow to be selectively interposed within or without the line of sightof the patient 15, or movable in the sense that a variable focal lengthlens can be used, with its optical characteristics being variable inaccordance with principles known in the art, for example those utilizedin various designs of autorefractors. That is, the test lens 22 can be,but not limited to, a single concave convex lens, or a combination ofoptical components, including a cylindrical lens and a prism.

[0027] As also shown, a light source such as but not limited to a laser24 generates a light beam 26 that can be directed, in one preferredembodiment, toward a laser beamsplitter 28. The laser beamsplitter 28reflects the light beam 26 toward the primary beamsplitter 20, which inturn reflects the beam through the test lens 22 and onto the eye of thepatient.

[0028] The beam 26 is then reflected by the eye of the patient 15, backthrough the lens 22, and is reflected off the primary beamsplitter 20.The beam passes through the laser beamsplitter 28, and a portion of thebeam is reflected off a pupil detection beamsplitter 30 toward a pupillight detector 32 through one or more focussing lenses 33, for purposesto be shortly disclosed. A portion of the return beam passes through thepupil detection beamsplitter 30 and propagates through an optical relayunit 34, which focusses the beam onto a wavefront analyzer optics 36.The wavefront analyzer optics 36 generates a signal representative ofthe wavefront of the return beam, and a wavefront detector 38 transformsthe signal into an electrical signal for analysis by a processor 40. Inone preferred embodiment, the processor 40 can be associated withcontrol electronics known in the art for undertaking control of one ormore components (e.g., the light source 24) of the system 10 as morefully set forth below. Also, the processor 40 can generate thebelow-described visual indications of the patient's vision as correctedby the test lens 22 and can cause the indications to be displayed on adisplay 42, such as a video monitor, that can be mounted on the housing12 or apart therefrom. Or, the display 42 can be a liquid crystaldisplay that can be mounted on the housing 12 of the system 10, or astandalone display unit conveniently located for the examiner's viewing.Suitable displays may include, but not be limited to, numerical and/orgraphical representations indicative of the patient's quality of vision,more details are provided in the following.

[0029] If desired, an illumination light 44, e.g., a ring-shaped fiberoptic, can be mounted on the housing 12 and can be connected to theprocessor 40 to control the pupil size of the patient 15. Theillumination light 44 can be a source of diffused light. The lightintensity of the illumination light 44 is controlled by the processor 40in response to feedback from the pupil light detector 32, which cancomprise a CCD camera, or reticon detector arrays to monitor the size ofthe pupil, so that a predetermined pupil size can be maintained for thepatient during the measurement. The locations of the pupil detectionunit, including the components, beamsplitter 30, lens 33, and pupillight detector 32 can be in other appropriate locations along theoptical path of the return light from the eye, including locationsinside the optical relay unit 34.

[0030] As a further improvement to the accuracy of the refractionmeasurement, the system also monitors the first Purkinge image, an imageformed by reflection at the anterior surface of the cornea of the lightbeam 26. The position of this image relative to the pupil boundary is anindication of gazing direction of the patient under examination. Unlessthe patient has strabismus in that eye, the relative position of theFirst Perkinge image is a well defined bright spot, and it is typicallyinside the pupil boundary. Therefore, in a preferred but non-limitingembodiment, the pupil detector 32 can also function as a patient gazingmonitor. In this case, the relative position of the First Perkinge imageto the pupil is determine by processing of the image data from the CCDcamera, for example, using data filtering, contrast enhancement, andpupil boundary determination methods known in the art.

[0031] All software processing can be done in real time in a matter of afraction of a second. The objective of this analysis is to determinewhether the patient is looking at the target, or momentarily driftingoff. The information is electromagnetically transmitted to the centralcontrol unit 40. If the patient is not looking at the target, the dataset from the wavefront detector unit 38 is rejected, and shall not bedisplayed or accumulated for data analysis.

[0032] The following comments are germane to implementation details ofpreferred, non-limiting embodiments. The light source 24 can be a diodelaser that emits light at near infrared wavelengths. Moreover, the lightdetectors 32, 38 can be implemented by CCD arrays or linear reticonarrays. Further, the primary beamsplitter 20 can be coated to transmitvisible light and to reflect infrared light. On the other hand, thelaser beamsplitter 28 can be a polarization dependent reflector, inwhich case the laser light is polarized, and a quarter wave plate (notshown) is disposed in the beam path to the patient 15 such that thereturn beam is rotated ninety degrees (90°) upon double passing thequarter wave plate for facilitating passage thereof through the laserbeamsplitter 28 toward the wavefront analyzer optics 36. Alternatively,the laser beamsplitter 28 can be plate coated for high transmission andlow reflectivity at forty five degrees (45°) incident angle, such thatonly a small portion of the laser light is reflected into the eye, but ahigh percentage of the return light propagates through the laserbeamsplitter 28.

[0033] Continuing with the implementation details of a preferred,non-limiting embodiment, the optical relay unit 34 can include twoconvex lenses F1 and F2 that together establish a telescope. The lensesF1, F2 are separated from each other by a distance equal to the sum oftheir focal lengths, with the focal plane of the first lens F1 beinglocated at the front surface of the test lens 22, i.e., the surfacefacing the primary beamsplitter 20. The focal plane of the second lensF2 is located at the image plane of the wavefront analyzer optics 36.The purpose of the telescope structure of the relay unit 34 is to relaythe wavefront at the exit surface of the test lens 22 to the image planeof the wavefront analyzer optics 36. Alternative relay optics can beused to achieve the same purpose.

[0034] With respect to the non-limiting details of the wavefrontanalyzer optics 36, the optics 36 can include an array of lensletsarranged as in a Shack-Hartmann wavefront sensor, an example of whichcan be found in page 37, “Customized Corneal Ablation The Quest forSuper Vision” edited by MacRae, et. al. published by Slack Incorporated,2001, incorporated herein by reference. Various Shack-Hartmann wavefrontsensors and processors are available, for example, from commercialvendors such as Wavefront Sciences, in Albuquerque, N. Mex.,Zeiss/Humphrey Instruments, in Dublin, Calif., or Bausch and Lomb, inIrvine, Calif. More preferably, the optics 36 can include ruled reticlessuch as those disclosed in co-pending application U.S. patentapplication Ser. No. 10/014,037, entitled “SYSTEM AND METHOD FORWAVEFRONT MEASUREMENT”, filed Dec. 10, 2001, incorporated herein byreference, which uses a self-imaging diffraction principle to detect thewavefront in the return beam.

[0035] Regardless of the type of wavefront analyzer optics 36 used, theprocessor 40 analyzes the profile of the wavefront of the light returnedfrom the patient's eye, and quantifies the wavefront aberrations in tworegimes: low order aberrations, including spherical refractive error,cylinder, and axis, and higher order aberrations, including coma,spherical aberrations and other higher order terms that can be describedby Zernike polynomials. Quantitative data representing the patient'squality of vision are then graphically presented on the display 42.

[0036] Now referring to FIG. 4, an exemplary mode of operation of thepresent invention can be seen. The patient 15 views the target 18through the phoropter system 10, and in particular through thetransparent window that is established by the primary beamsplitter 20.At block 44 the examiner initiates the vision test by inserting aselected test lens 22 in the line of sight of the patient, or byconfiguring a variable focal length lens 22 to have a predeterminedfocal length. Inserting means either a manual positioning or positioningusing a motorized means. Or, the processor 40 can select a particularlens 22 and cause it to be automatically moved in the line of sight, inaccordance with disclosure below.

[0037] Proceeding to block 46, the processor 40 determines the pointspread function (PSF) that is derived from using, for instance, theterms of Zernicke polynomials, which is in turn derived from thewavefront passing through the wavefront analyzer optics 36 andtransformed into an electrical signal by the wavefront detector 38 atthe instant when the wavefront data is acquired. The processor 40Fourier transforms the signal from the wavefront detector 38 using thefollowing equation:

PSF(x, y)=FT(P(x, y))|²

[0038] wherein FT designates a Fourier Transform calculation and P(x, y)is the spatial distribution of the wavefront profile of light with thesame phase (phase front) returned at the corneal plane.

[0039] Proceeding to block 48, if desired an Optical Transfer Function(OTF) can be calculated from an inverse operation of Fourier Transformas follows:

OTF(f _(x) , f _(y))=FT ⁻¹(PSF(x, y)),

[0040] wherein f_(x), f_(y) are spatial frequencies in x and ydirections, respectively, that are orthogonal to each other.

[0041] Moreover, a Modular Transfer Function (MTF) can be determined asthe amplitude of the OTF:

MTF(f _(x) , f _(y))=|OTF(f _(x) , f _(y))|.

[0042] The above functions are used to generate visual indications ofthe quality of vision that is afforded by the test lens 22 currentlybeing viewed by the patient 15. For instance, once the PSF is determinedat block 46, the logic can flow to block 50 to determine a convolutionalfunction G as follows:

G(ximg, y _(img))=∫∫PSF(x−x _(img) , y−y _(img))f(x _(img) , y _(img))dxdy,

[0043] wherein f(x_(img), y_(img)) is the test target 18 (FIG. 3), i.e.,an ideal image function, x−x_(img) is the difference in the x-dimensionbetween each point in the PSF and the corresponding ideal point in theideal image, and y−y_(img) is the difference in the y-dimension betweeneach point in the PSF and the corresponding ideal point in the idealimage.

[0044] The convolutional function G can be used at output state 52 togenerate an appropriately blurred image, point by point, of an idealimage as affected by the imperfection of the patient's eye incombination with the lens 22. For example, when the target 18 is aSnellen chart, the ideal image function can be the letter “E” or aseries of other letters, e.g., of various physical sizes asconventionally used in the various lines in the Snellen chart. FIG. 5shows one such blurred image at 54, which can be presented on thedisplay 42. Alternatively, the target can be a picture, and theconvoluted image G(x_(img), y_(img)) of the picture is blurred point bypoint, according to the PSF, which represents an image of the targetformed at the patient's retina.

[0045] Accordingly, the letters in the simulated blurred image have thesame blurring as perceived by the patient 15. In this way, the examinercan visualize the clarity and sharpness of the image as a result of thelens 22 as it is perceived by the patient 15.

[0046] Alternatively or in addition to the image shown in FIG. 5, theprocessor 40 can generate the displays shown in FIGS. 6-8 as follows. Atblock 56 the wavefront profile, as indicated by the above-mentionedlinear combination of Zernike polynomials, is filtered to eliminateterms with coefficient below a threshold amplitude. Moving to block 58,a psychometric weighting factor “P” is inserted for each of theremaining Zernike terms as shown in the following. This weighting factor“P” represents the effect of the brain to discriminate objects despitecertain types of ocular aberrations. For example, most people candiscern a letter in a Snellen chart with a certain amount of defocuswhile the same amplitude of aberration in coma would not allow the samepatient to discern that letter. To compensate for this, a Quality ofVision Factor (QVF) is determined as follows:

QVF=exp−(Σ_(n) P _(n) Z _(n) ²)

[0047] wherein P_(n) is the psychometric weight factors for thecorresponding n^(th) term of the Zernike polynomials, and Z_(n) is thecoefficient of the n^(th) term of the Zernike polynomials in the PSF.

[0048] The psychometric weighting factors “P” can be determined bypresenting a particular aberration to a normative group of people, forexample, between one hundred to four hundred people, depending on theaccuracy level desired and the range of the scatter value of each typeof aberration measurement. The patients are presented one at a time withparticular types of aberrations selected from the Zernike polynomials,and then the patients are scored for the extent of success in discerningthe target, for example, by the number of letters correctly read on theSnellen chart, or other standardized vision test chart. Other scoringmethods base on contrast level, standardized letter size, sine or squarewave patterns can also be used as targets.

[0049] The presenting means can be an aberration plate on which aselected type of aberration has been imprinted. For example, theaberration type can be a coma, or a trefoil, having the refractive indexprofile as specified by the corresponding Zernike polynomial.

[0050] The relative effect of each type of aberration is tabulated forthe group and averaged to obtain statistically meaningful weightfactors. For most practical purposes, Zernike coefficients for termshigher then the sixth order (term number twenty nine or higher)minimally contribute to the overall aberration profile of normal eyes.The method of producing various types of aberrations with desiredamplitudes according to each of the Zernike terms is set forth inco-pending U.S. patent application Ser. No. 09/875,447 filed Jun. 4,2001, incorporated herein by reference. In the event that no data forthe psychometric weight factors are available, all weighting factorsP_(n) can be set to unity.

[0051] Once the QVF has been determined, one or more of the displaysshown in FIGS. 6-8 can be generated and displayed as indicated in block60. For example, as shown in FIG. 6, a bar chart display can begenerated to present an overall indication of the patient's quality ofvision as afforded by the lens 22 under test. As shown, the indicatorcan be in the form of a graduated bar 62, the height of which isproportional to the QVF determined at block 60, with zero indicatingpoor vision and perfect vision being indicated by a bar extending fromthe bottom to the top 64 of the scale. If desired, the display scale canbe a log scale, in which case the “best” is indicated by the bar 62being at zero, and rising logarithmetrically with worse vision using aroot-mean-square function of the QVF. Enhancements to the bar 62 such ascolor-coding can be used. For instance, the bar 62 can be colored redfor poor vision and green for good vision, with other colors being usedto indicate intermediate qualities of vision. In lieu of the bar chartof FIG. 6, the QVF can be used to generate a pie chart as shown in FIG.7, with the size of a pie slice 66 relative to the entire circle beinglinearly or logarithmetrically proportional to the QVF.

[0052] The system 10 can continuously measure the wavefront profile ofthe light beam returned from the patient's eye. Accordingly, in onepreferred, non-limiting embodiment, a sequence of QVF measurements(e.g., twenty) for a single test lens 22 can be made in a second or twoand grouped together.

[0053] As described earlier, the measurement accuracy can be improved bymonitoring the gazing direction of the patient, and the computing devicein block 40 can reject the data points acquired when the patient was notlooking at the designated target. Furthermore, the computing device canalso accumulate data and perform calculations for average values andstandard deviation for selected subsets of measurement.

[0054]FIG. 8 shows a resulting display. As can be appreciated from theexemplary embodiment shown, five lenses 22 have been tested and severalQVF values obtained over a short period for each. Each group of QVFvalues is plotted as a respective vertical line 68 on a plot of QVFversus lens, with the length of each error bar line 68 representing thestandard deviation of the measurements for that particular lens and thecenter of each line representing the mean QVF value. The prescriptioncan be based not only on a high mean QVF value, as indicated at points70 and 72, but also on a small standard deviation, as indicated by bar74. That is, the lens corresponding to the bar 74 might be selectedbecause its QVF values had a small standard deviation from each otherand it had a high mean QVF value, even if not as high as the point 70.This recognizes that some patients prefer a lens power which may notnecessarily provide the sharpest image but which does result in morecomfort, since a patient does relatively little searching for the“better focus” using lenses that exhibit smaller standard deviations inthe QVF. For example, a patient did not have a vision check for anextended period of time, and the required correction is more than 1.5diopters in cylinder, for example. The patient may feel uncomfortablewith the full correction as afforted by the sharpest image, rather thepatient prefers a smaller amount of correction which representsimprovement in his vision, yet not causing dizziness or head strains.Therefore, the present invention provides objective data based on thesubjective response of the patient to a test lens set 22 presented tothe patient.

[0055] As recognized by the present invention, to diagnose a patient'scontrast, the patient can be presented with a series of standardizedpatterns of sine wave gratings of increasing spatial frequencyfrequencies, with the patient offering subjective responses. Theresulting examination report can be a curve that depicts a cutoffcontrast intensity at various spatial frequencies. The present inventioncan provide a quantitative evaluation of a patient's contrast, which canbe generated in addition to or in lieu of those displays disclosedabove. Such a display can be generated at output state 76 in FIG. 4 andis shown in FIG. 9, showing a curve 78 depicting actual patient opticalcontrast function (OCF) and a reference curve 80 depicting adiffraction-limited reference. To determine OCF, the following relationis used.

OCF=MTF×M _(lat).

[0056] wherein MTF is the modular transfer function determined at block48 and M_(lat) is a mathematical function accounting for the lowfrequency filtering of the neural system, the value of which linearlyincreases with spatial frequencies with a slope of unity in a log-logscale plot and reaching the maximum value of one at and above thespatial frequency of seven cycles per degree.

[0057] Accordingly, the OCF does not include the effect of the brainprocessing at frequencies higher than seven cycles per degree, but itdoes provide valuable information about the patient's ability to discernsine gratings of various spatial low frequencies based on a patient'soptics.

[0058] The above process of measuring and displaying indications of theimprovement in vision afforded by a particular test lens 22 to thepatient 15 can be continued at block 82 until the “best” test lens isfound. This can be done by the examiner manually swapping lenses 22 asin a conventional phoropter, or, as mentioned above, the positioning oftest lenses 22 can be done automatically by the processor 40 controllingthe moving mechanism “M”, which can include a motor and couplingstructure connecting the motor to one or more lenses 22, such that themechanism follows an instruction from the processor 40 to insert theparticular lens in the line of sight of the patient, as requested by theprocessor.

[0059] When done by the processor 40, the sequence of test lenses 22 tobe used in an examination may be programmed into the processor 40 inaccordance with examination strategy and routines known in the art. Thestarting lens can be selected based on the patient's current spectacleprescription or based on the wavefront measurement without any test lens22 in the patient's line of sight. Consequently, in reconstructing thereturn beam wavefront without a test lens 22 being in the beam path, theprocessor 40 essentially models the uncorrected aberrations of thepatient's eye in Zernike terms. Recall that the second order Zerniketerms represent defocus, astigmatism and axis information. Based on thepatient's pupil size and the uncorrected wavefront error amplitudes, theprocessor 40 can determine the equivalent diopter power in sphere andcylinder and its axis, and select the appropriate lens 22 being used tostart the examination. In selecting test lenses 22, the processor 40 canuse the above-disclosed QVF values in lieu of subjective responses fromthe patient, and can then execute the examination strategy as if it isperformed with the subjective response from the patient.

[0060] The automatic refraction process is depicted in FIG. 10, andgenerally designated 100. Process 100 begins with a first step 102wherein the patient looks at a target. In step 104 a test lens ispositioned between the target and the patient's eye, and in the line ofsight of the patient. A light beam is directed through the test lens andinto the patient's eye in step 106. A portion of that light is reflectedfrom the surfaces within the eye and returns along the line of sight ofthe patient.

[0061] In step 108, the light returning from the patient's eye isdetected. From this detected light, the wavefront profile may bereconstructed, as shown in step 110. From the reconstructed wavefrontprofile, the quality vision factor (“QVF”) may be calculated in step112. In order to improve the accuracy of the measurements of thepatient's eye, “N” number of measurements are performed using thereturning light. Thereby, “N” wavefront measurements are taken, therebyyielding N wavefront profiles and corresponding QVF values. Thesesuccessive measurements are taken by returning from step 112 to step108, in which the returning light is again detected “N” times.

[0062] Once “N” measurements have been taken and the QVF for eachmeasurement has been calculated, the QVF for that particular test lens,is analyzed in step 114. The analysis of this data provides for adetermination that the correction with that particular lens is optimal.This decision is made in step 116, and if the correction is not optimal,a next test lens is selected in step 120, and the process returns tostep 104 where the next test lens is positioned in the patient's line ofsight. On the other hand, if the correction with that particular lens isoptimal, than the process ends in step 122 resulting in the properrefractive correction having been identified.

[0063] In a typical automatic refraction process, a series of lenses in¼ diopters increments are used to determine the patient's opticalcorrection. However, the present invention contemplates using more orless than the typical number of lenses, and the diopter increments canbe in ⅛ instead of ¼, depending upon the magnitude of correctionnecessary. Also, as shown in FIG. 10, a number (“N”) of measurements ofthe returning light are taken in steps 108 through 112 to calculate theVQF for the particular test lens. Typically, “N” will equal for example,10-20 separate measurements being taken to provide an accuratemeasurement of the VQF. However, the present invention contemplatestaking more or less than the typical number of measurements dependingupon the particular wavefront sensor device used, and the magnitude ofcorrection necessary.

[0064] The prescription can be determined by a person viewing thedisplay of FIG. 8, or automatically by the processor 40 based on a highQVF value and low standard deviation, as follows: The examiner, or theprocessor will examinate the curve shown in FIG. 9, which connects theaverage values of the QVF's for various lens sets presented to thepatient. An improvement may include the step of performing a best fit tothe average values, suing a polynomial of up to 4 order, for example.The processor searches for the maximum value, of the “peak” of thecurve. This can be accomplished by monitoring the peak value of thecurve, or slope of the curve from decreasing lens power, from right toleft, in FIG. 8. When the curve reaches its maximum value, the slopechanges sign, and the maximum is at the zero slope value. Now, theprocessor send the peak value of the QVF and the corresponding lenspower to the display or a printer.

[0065] Additionally, the processor also searches for the minimum valueamong the standard deviation in the data set as shown in FIG. 8. Afigure similar to FIG. 8 showing standard deviations versus lens powercan be useful (not shown) in determining the minimum value, suing thesteps of a best fit curve, and search for the sign change of the slopeas described above for determining the maximum QVF value. Again, thisminimum standard deviation value and the corresponding lens power aresent to the display or a printer for record. For example, on the displayor the printout the processor may indicate that lens power with themaximum QVF value provides for the sharpest image, while the lens powerwith the minimum standard deviation provides for the most comfortableprescription to the patient.

[0066] While FIG. 3 illustrates a system 10 wherein the return beam fromthe lens 22 is detected and analyzed and, hence, the integrated effecton the wavefront introduced by the eye and lens 22 is measured, it is tobe understood that as mentioned above the return beam from the eye canalso be analyzed without passing through the lens 22. In such anembodiment, the effect of the lens 22, which has a known deviation fromspherical, can be accounted for by adding or subtracting the lens 22effect as appropriate from the eye-only wavefront. To facilitate this, asensor (not shown) can be provided that senses which lens 22 is movedinto the patient's line of sight. The sensor sends a signalrepresentative of the lens (and, hence, of the optical contribution ofthe lens) to the processor 40.

[0067] In any case, it may now be appreciated that if desired, theexaminer can use conventional tactics in the steps of selecting testlenses 22 as if the whole process were done using a conventionalphoropter that requires subjective responses from the patient. Forexample, the examiner can use “fogging” in accordance with principlesknown in the art to form an artificial image before the retina of thepatient to cause the patient to relax the above-mentioned accommodativepower. However, owing the present display capability of the system 10,the examiner can identify the test lens 22 with which the patientachieves good vision without accommodation, regardless of patient verbalcooperation or ability to judge and articulate which lens 22 is best.That is, by observing the present displays and continuing to decreasethe focusing power of the test lenses being used and moving the imagebehind the patient's retina, the examiner can determine the range ofaccommodation of the patient.

[0068] Once the best lens 22 has been identified, the examiner mayindicate this decision by pressing a “finish” button (not shown), and aprintout of the examination result can be output using a printer orsimilar device (not shown) that is connected to the processor 40. Theprocessor 40 may also automatically transmit via modem, internet orother appropriate means, the prescription to a remote location for lensmanufacturing. A prescription to correct low order aberrations includingsphere, cylinder and axis, can be used for prescribing conventionalophthalmic lenses, or a “supervision” prescription to correct all ordersof aberrations can be used to prescribe improved vision lenses, such asare described in co-pending U.S. patent application Ser. No. 10/044,304,filed Oct. 25, 2001 and incorporated herein by reference.

[0069] While the particular APPARATUS AND METHOD FOR DETERMININGOBJECTIVE REFRACTION USING WAVEFRONT SENSING as herein shown anddescribed in detail is fully capable of attaining the above-describedobjects of the invention, it is to be understood that it is thepresently preferred embodiment of the present invention and is thusrepresentative of the subject matter which is broadly contemplated bythe present invention, that the scope of the present invention fullyencompasses other embodiments which may become obvious to those skilledin the art, and that the scope of the present invention is accordinglyto be limited by nothing other than the appended claims, in whichreference to an element in the singular is not intended to mean “one andonly one” unless explicitly so stated, but rather “one or more”. Allstructural and functional equivalents to the elements of theabove-described preferred embodiment that are known or later come to beknown to those of ordinary skill in the art are expressly incorporatedherein by reference and are intended to be encompassed by the presentclaims. Moreover, it is not necessary for a device or method to addresseach and every problem sought to be solved by the present invention, forit to be encompassed by the present claims. Furthermore, no element,component, or method step in the present disclosure is intended to bededicated to the public regardless of whether the element, component, ormethod step is explicitly recited in the claims. No claim element hereinis to be construed under the provisions of 35 U.S.C. §112, sixthparagraph, unless the element is expressly recited using the phrase“means for” or, in the case of a method claim, the element is recited asa “step” instead of an “act”.

What is claimed is:
 1. An apparatus for determining the refraction andaberrations of a patient's eye, comprising: a light source; opticsdirecting light from said light source to the patient's eye; at leastone test lens disposable into a line of sight defined between a patientand a target, such that a patient looking at a target perceives lightfrom said light source through the lens; and at least one wavefrontmeasurement device positioned to detect aberrations in light returningfrom the patient's eye, the aberrations being caused at least partiallyby an eye of the patient.
 2. The apparatus of claim 1, furthercomprising a housing containing said wavefront measurement device havinga substantially transparent window through which the patient looks atthe target.
 3. The apparatus of claim 1, wherein the light sourceincludes a laser for generating the light.
 4. The apparatus of claim 1,wherein the wavefront measurement device includes at least one lightdetector receiving a wavefront from the light returning from thepatient's eye, and outputting a signal representative of theaberrations.
 5. The apparatus of claim 4, further comprising at leastone visual display generated instantaneously by the processor partiallyusing the diagnostic signal from the light detector, the displaycomprising at least one from the list: (1) an image generated by aconvolution of the image of the target based on the wavefront returningfrom the patients eye and through the test lens; (2) a numerical and/orgraphic display representative of the effectiveness of the test lens;(3) a numerical and/or graphic display of the contrast function of thepatient's vision.
 6. The apparatus of claim 1, wherein said targets areat a predetermined distance from the patient.
 7. The apparatus of claim4, wherein the wavefront measurement device includes at least oneprocessor receiving the signal from the light detector and outputting atleast one diagnostic signal representative thereof.
 8. The apparatus ofclaim 7, wherein the processor outputs said diagnostic signal instantly,and wherein said diagnostic signal corresponds to the objectiveassessment of quality of vision.
 9. The apparatus of claim 8, whereinsaid objective assessment of quality of vision is useful for generatingan image representative of the target.
 10. The apparatus of claim 8,wherein the diagnostic signal is useful for generating at least onevisual display representative of an effectiveness of the lens incorrecting a patient's vision.
 11. The apparatus of claims 9 or 10,wherein said processor uses said objective assessment of quality ofvision to select a next lens to determine a successive objectivemeasurement of quality of vision corresponding to said next lens. 12.The apparatus of claim 7, wherein said processor determines the standarddeviation of said objective measurement of quality of vision and one ormore successive objective measurements of quality of vision andidentifies an optimal vision correction lens for the patient.
 13. Theapparatus of claim 5, wherein the visual display includes at least oneof: a bar chart, a pie chart, and a line chart.
 14. The apparatus ofclaim 5, wherein the visual display is color coded.
 15. A method forindicating the quality of a patient's vision, comprising: providing aphoropter through which a patient can look at a target spaced from thephoropter; directing a laser beam into an eye of a patient when thepatient looks into the phoropter; detecting aberrations in a wavefrontof the light beam as the light beam returns from the patient's eye; andat least partially based on the detecting act, indicating a quality of apatient's vision.
 16. The method of claim 15, further comprisingassociating at least one test lens with the phoropter, positioning thetest lens in the patient's line of sight, the wavefront being detectedafter the laser beam returning from a patient's eye passes through thetest lens.
 17. The method of claim 15, wherein the act of indicatingincludes generating an image of the target at least partially based onthe wavefront.
 18. The method of claim 15, wherein the act of indicatingincludes generating at least one visual display representative of aneffectiveness of the lens in correcting the patient's vision.
 19. Themethod of claim 18, wherein the visual display comprises at least onefrom the list: (1) an image generated by a convolution of the image ofthe target based on the wavefront returning from the patients eye andthrough the test lens; (2) a numerical and/or graphic displayrepresentative of the effectiveness of the test lens; (3) a numericaland/or graphic display of the contrast function of the patient's vision.20. The method of claim 18, wherein the visual display includes at leastone color-coded display.
 21. The method of claim 19, further comprisingdetermining the refraction for the patient.
 22. The method of claim 21,further comprising: evaluating the display representing theeffectiveness of the lens; selecting a second test lens set from thelenses; positioning said second test lens in the patient's light ofsight; and generating at least a second visual display representative ofan effectiveness of the second test lens in correcting a patient'svision.
 23. The method of claim 22, wherein said visual display isgenerated substantially instantaneously following positioning of thesecond test lens in the patient's line of sight.
 24. The method of claim21, wherein the determining further comprises prescribing ophthalmiclenses for the patient.
 25. The method of claim 24, wherein prescribingfurther comprises dispensing ophthalmic lenses for correcting therefractive errors of the patient based on either (i) the low orderaberrations including the sphere, cylinder and axis, or (ii) low orderaberrations in (i) and the higher order aberrations including the thirdorder and higher Zernike terms.
 26. The method of claim 22, wherein theselecting of a second test lens comprises determining at least one ofthe following: (a) the onset of the patient's accommodation, and (b) therange of the patient's accommodation.
 27. The method of claim 22,wherein the selecting of a more suitable trail lens comprises “fogging”the patient.